Angled drilling is necessary and useful wherever drilling holes have to be made starting from narrow spaces. These holes usually require a length longer than the geometric measurements of the spaces. In the case of narrow limitations where two space coordinates in whose plane the drill hole (s) have to be made, there is enough room in the direction of the third coordinate perpendicular to this plane for the drilling device and its' advance, which has to correspond to the depth of the drilling hole.
For the above-mentioned reasons, angled drilling is particularly suitable in mining and tunnel construction. This suitability derives from the space limited cross section of mining and tunnel galleries which in most cases is coupled with sufficient length, for instance in shafts, blind shafts, galleries, tunnels, rises and struts.
Devices have been known for many years which drill holes from an angled position with respect to the drilling hole axis. These devices have attempted to overcome the afore-described difficulties, especially in mining and tunnel construction, to produce drilling holes out of narrow spaces, holes whose length is considerably bigger than the measurements of the underground spaces. All these efforts have up to now however not been successful. These failures have been due to process disadvantages and to relatively high costs. None of the devices heretofore known have been suitable for industrial use.
A known drilling process, which has not yet yielded successful results after years of industrial testing, has a particularly "flexible shaft" consisting of two oppositely twisted wire springs with special wire diameter, lodged one within the other. Usually this shaft can be angled. During the transmission of torque required for drilling, the inner spiral is supposed to widen, while the diameter of the outer spiral is supposed to decrese. As a result, a certain stiffening effect is supposed to occur. However, this theoretically established modus operandi did not perform well in practice for industrial use, even after many years of attempts and of successive improvement stages.
Another process is based on the idea to produce drilling holes with the aid of the "maximum-pressure water technique" (HDW-German abbreviation). Maximum-pressure hoses are flexible and because of this seem to be suited for angled drilling. Rotary transmissions, have been developed which theoretically have potential for long service life, in spite of the high strain they are subjected to. At this point of development, the process could be expected to produce good results in industrial testing. Although with the principle of HDW-drilling it is possible for the first time to expect in all pobability an industrially applicable process for an angled drilling of drill holes, it is still necessary to accept a series of technological and cost disadvantages. Although the HDW-technique has many advantages, it does not allow for drilling holes with smooth wallings. For this reason, this technique is mainly suited for the production of armature holes, but less for the production of shot holes. In the exclusive drilling with maximum-pressure water, based on present knowledge, the drilling advance will not be unsubstantially less than the drilling advance in the case of rotary or rotary percussion drills. Besides, when drilling exclusively with maximum-pressure water there results during the drilling time a very considerable volume of water and detritus flow for which separate evacuation installations have to be provided. A large detritus flow arises because rocks surrounding the mining area often are sensitive to water and under its influence experience a decrease in their solidity.